A power inductor for use in a power supply circuit is required to achieve smaller size and lower loss and cope with a large current. With a view to meeting such requirements, it is being studied to use, as a magnetic material for the power inductor, a metal magnetic material having a high saturation magnetic flux density. Although the metal magnetic material has an advantage of exhibiting a high saturation magnetic flux density, an insulation resistance of the material itself is insufficiently low. Thus, as a prerequisite for allowing the metal magnetic material to be used as a magnetic material for an electric component, it is necessary to ensure insulation between particles of the metal magnetic material. If it fails to ensure the insulation, a component body of the electric component is electrically conducted to surroundings, or material properties of the metal magnetic material are degraded, thereby leading to an increase in loss in an end product.
Therefore, in order to allow the metal magnetic material to be used for an electric component, the insulation between particles of the metal magnetic material has heretofore been ensured by bonding the particles together by a resin or the like or by coating each of the particles with an insulating film.
For example, JP 2010-062424A describes an electronic component obtained by coating a surface of a Fe—Cr—Si alloy with ZnO-based glass to prepare a metal magnetic material, and subjecting the material to burning in a vacuum or oxygen-free or low-oxygen partial pressure atmosphere. However, the burning in a vacuum or oxygen-free or low-oxygen partial pressure atmosphere gives rise to a need to ensure coating of particles of the metal magnetic material so as to prevent sintering. This leads to problems such as a need to increase an addition amount of the glass, and an increase in cost for coating the particles.
As above, the conventional technique of bonding the particles together by a resin or the like or coating each of the particles with an insulating film has a problem that the amount of an insulating material other than the metal magnetic material has to be increased so as to more reliably ensure insulation performance, and the increase in volume of a material other than the metal magnetic material leads to degradation in magnetic properties.
There has also been disclosed a technique of forming a layer of an oxide originating from only a raw material composition of particles of a metal magnetic material, on each of the particles (JP 4866971B and JP 5082002B). In this technique, an insulation film made of an oxide originating from only the raw material composition of the particles of the metal magnetic material is utilized for insulation between the particles, so that degradation in magnetic properties becomes reduced. However, in some cases, such an insulating film made of an oxide originating from only a raw material composition of particles of a metal magnetic material, as used in the above technique, exhibits poor insulation performance or fails to obtain sufficient strength.
Therefore, there has also been disclosed a technique of forming a layer of an oxide originating from only a raw material composition of particles of a metal magnetic material, on each of the particles, and then impregnating the layer with a resin (JP 2012-238841A). However, the technique based on the impregnation or the like is poor in practicality because it causes not only an increase in cost but also a lack of stability in product quality.
Further, JP 2013-033966A discloses a magnetic layer material containing: metal magnetic particles each having a core-shell structure in which a core is made of an iron-based compound, and a shell made of a metal compound is formed around the core; and glass. However, this technique is required to coat the core-forming material with the shell-forming material so as to construct the core-shell structure. Thus, as with the aforementioned conventional technique of coating each particle with an insulating film, there are problems such as an increase in cost, and an increase in amount of a coating material (shell-forming material), leading to degradation in magnetic properties.
In the metal magnetic material for an electronic component, particles thereof need to be mutually insulated by a minimum insulating layer, so as to ensure high insulation performance. Further, the insulating film needs to be strong electrically and mechanically. Furthermore, a composition in each particle of the metal magnetic material needs to be maintained uniformly. However, each of the conventional techniques has some sort of problem, as mentioned above.